1. Field of the Invention
The present invention is related to an artificial heart valve frame. More specifically, the present invention is directed to an artificial valve prosthesis.
2. Background Art
The mitral valve is a functional organ composed of multiple dynamically interrelated units. During cardiac cycle, the fibrous skeleton, the anterior and posterior leaflets, the papillary muscles, the chordae tendinea, and the ventricular and atrial walls all interplay to render a competent valve. The complex interaction between the mitral valve and the ventricle by the subvalvular apparatus (the papillary muscles and the chordae tendinea) is essential in maintaining the continuity between the atrio-ventricular ring (which is part of the fibrous skeleton of the heart) and the ventricular muscle mass, which provides for the normal functioning of the mitral valve.
Cardiac valves, including the mitral valve, exhibit two types of pathologies: regurgitation and stenosis. In the case of the mitral valve, regurgitation is the abnormal leaking of blood from the left ventricle, through the mitral valve, and into the left atrium, when the left ventricle contracts. Stenosis is the narrowing of the orifice of the mitral valve of the heart. Regurgitation is the more common of the two defects. Either defect can be treated by a surgical repair. However, surgical procedures can lead to an interruption of the mitral annulus-papillary muscle continuity, which accounts for changes in geometry mechanics and performance of the left ventricle. These problems are lessened by the emerging techniques for minimally invasive mitral valve repair, but still many of those techniques require arresting the heart and funneling the blood through a heart-lung machine, which can also be traumatic for patients.
Under certain conditions, the cardiac valve must be replaced. Standard approaches to valve replacement require cutting open the patient's chest and heart to access the native valve. Such procedures are traumatic to the patient, require a long recovery time, and can result in life threatening complications. Therefore, many patients requiring cardiac valve replacement are deemed to pose too high a risk for open heart surgery due to age, health, or a variety of other factors. These patient risks associated with heart valve replacement are lessened by the emerging techniques for minimally invasive valve repair, but still many of those techniques require arresting the heart and passing the blood through a heart-lung machine.
In addition, valve replacement can create additional problems including limitation of the mitral flow during exercise due to a small effective orifice area and high cardiac output imposed by a smaller size artificial valve. Further, the rigid structure of an artificial valve prevents the physiologic contraction of the posterior wall of the left ventricle surrounding the mitral annulus during systole. Also, myocardial rupture can result from excision or stretching of the papillary muscle in a thin and fragile left ventricle. Additionally, chordae rupture can also occur due to the chordae rubbing against the artificial valve over time, leading to increased heart wall stress. It has been shown that severing the chordae can lead to a 30% reduction in chamber function. Thus, mitral valve replacement has a high mortality rate in very sick, chronic heart failure patients.
The chordae tendinea, which connect the valve leaflets to the papillary muscles (PM) act like “tie rods” in an engineering sense. Not only do the chordae tendinea prevent prolapse of the mitral valve leaflets during systole, but they also support the left ventricular muscle mass throughout the cardiac cycle. To function adequately, the mitral valve opens to a large orifice area and, for closure, the mitral leaflets have an excess surface area (i.e. more than needed to effectively close the mitral orifice). On the other hand, systolic contraction of the posterior ventricular wall around the mitral annulus (MA) creates a mobil D-shaped structure with sphincter-like function which reduces its area by approximately 25% during systole, thus exposing less of the mitral leaflets to the stress of the left ventricular pressure and flow.
It has been long postulated that the structural integrity of the MA-PM continuity is essential for normal left ventricular function. Recent evidence supports the concept that preservation of the subvalvular apparatus with the MA-PM continuity in any procedure on the mitral valve is important for the improved long-term quality and quantity of life following valve replacement. Maintaining the MA-PM continuity, thus, appears to provide a substantial degree of protection from the complications associated with valve replacement.
Efforts have been focused on percutaneous transluminal delivery of replacement cardiac valves to solve the problems presented by traditional open heart surgery and minimally-invasive surgical methods. In such methods, a valve prosthesis is compacted for delivery in a catheter and then advanced through a patient's vasculature to the heart, where the prosthesis is then deployed in the native valve annulus.
Therefore, what is needed is a mitral valve prosthesis and method of implantation that minimizes the traumatic impact on the heart while effectively replacing native leaflet function. A consistent, reproducible, and safe method to introduce a prosthesis into the mitral position in a minimally invasive fashion could be attractive for numerous reasons: a) it can treat both functional and degenerative mitral regurgitation (MR); b) it can treat mitral stenosis; c) it can offer a remedy to inoperable patients, high risk surgical patients, and those that cannot tolerate bypass; d) it can allow a broad range of practitioners to perform mitral valve procedures; and/or e) it can enable more consistency in measuring outcome.